work: Chapter 8 ... Saved Help Save Check my work A random sample of 12 items is drawn from a population whose standard deviation is unknown. The sample mean is a = 800 and the sample standard deviation is s = 10. Use Appendix D to find the values of Student's t. (a) Construct an Interval estimate of u with 95% confidence. (Round your answers to 3 decimal places.) The 95% confidence interval is from (b) Construct an Interval estimate of / with 95% confidence, assuming that s = 20. (Round your answers to 3 decimal places.) The 95% confidence interval is from (c) Construct an interval estimate of u with 95% confidence, assuming that s = 40. (Round your answers to 3 decimal places.) The 95% confidence interval is from (d) Describe how the confidence interval changes as s increases. O The Interval stays the same as s increases. O The interval gets wider as s increases. O The Interval gets narrower as s increases.